Streptococcus mutans, the principal etiologic agent of dental caries in humans, infects more than 95% of the population worldwide, often colonizing the oral cavity during the first year of life. Prominent among the attributes which contribute to S. mutans-induced caries formation is the metabolism of exogenous dietary carbohydrates; this results in the production of lactic acid in the oral cavity which leads to the demineralization of tooth enamel and the onset of dental decay. Exogenous carbohydrates represent only one source of S. mutans acid production, however. Alternatively, S. mutans can produce acid by metabolizing intracellular polysaccharides (IPS), glycogen-like storage polymers. Very little is known of S. mutans IPS and the mechanism(s) which regulate their expression in the plaque environment. Thus, an investigation of S. mutans IPS will extend our knowledge of the events which lead to acid production in the oral cavity and so provide novel treatment strategies for the prevention of tooth decay. The investigator identified and cloned the glycogen (glg) locus which is involved in S. mutans IPS accumulation and demonstrated that S. mutans IPS are significant contributors to the caries-forming process. Specifically, an IPS-deficient mutant which bears a deletion at the S. mutans glg locus is significantly less cariogenic than its wild-type progenitor in germfree rats, while a transposon mutant which accumulates IPS in excess of wild-type levels is significantly hypercariogenic in this animal model. The major goals of this research proposal are to elucidate the structural organization of the S. mutans locus and to investigate the mechanism(s) by which S. mutans IPS accumulation is regulated in the plaque environment. The specific aims include 1) the continued nucleotide sequence analysis of the S. mutans glg locus, 2) the characterization of glg gene expression in S. mutans grown in environments which approximate the oral cavity, 3) the identification of regulatory elements which govern S. mutans glg gene expression, and 4) the investigation of putative cross-regulation between the S. mutans glg operon and other genetic loci which contribute to sucrose metabolism in this oral pathogen. Indeed, these studies will further our understanding of the events which lead to acid production in the plaque environment by elucidating the regulatory network which operates to optimize the cariogenic potential of S. mutans.